This invention relates to a photothermographic material and more particularly, to a photothermographic material for laser exposure.
Typical prior art means for outputting the image information of medical diagnosis apparatus such as MRI and X-ray CT involves scanning photosensitive material with a laser beam for exposure. Semiconductor laser diodes featuring high output and stability are commonly used as a light source therefor.
Since a photothermographic system is free of a fixation step of dissolving away silver halide, the photosensitive material used therein must be free of haze. The silver halide grains must be reduced in size in order to minimize haze.
However, a photosensitive material comprising a microparticulate emulsion or having high transparency tends to produce interference fringes as a result of reflection of laser light in the interior of the material. As one solution to interference fringes, JP-B 10735/1994 discloses an improved photosensitive material, which is not successful in extinguishing interference fringes.
Attempts to extinguish interference fringes are also made on the laser scanning exposure system. JP-A 113548/1993 discloses a laser scanning exposure method of scanning a transparent layer with a laser beam at such an offset angle that no interference may occur between reflected light rays from upper and lower interfaces of the transparent layer. Interference fringes are not extinguished where there is more than one layer having a different refractive index from the support.